Final Report Summary - SACP (Role of Senescence-associated Cysteine Proteases)
Project objectives
The aim of the project was to identify proteases that are responsible for leaf senescence in plants, which involves a massive degradation of rubisco, the most abundant protein in the world. Remarkably, the proteases involved in this proteolytic process are not yet known. The approach was to use activity-based profiling with probes for proteases to identify the protease activities that are up-regulated during leaf senescence in Arabidopsis, and subsequently to address their role in senescence using reverse genetic approaches.
Probes for the proteasome, serine proteases and vacuolar processing enzymes did not reveal significantly increased activities of any of these enzymes during senescence. In contrast, probes for papain-like cysteine proteases showed an increased activity of some of these enzymes during senescence, predominantly caused by increased levels of one protease called RD21. Additional senescence-related proteases identified by mass spectrometry included SAG12, which is used as a transcriptional marker for senescence. Surprisingly, Arabidopsis mutants lacking RD21 or other senescence-related proteases did not have phenotypes in senescence assays, such as chlorophyll degradation, despite the fact that they have significantly reduced protease activities in senescing leaves.
These data suggest that these proteases act redundantly with other senescence-related proteases. Further work would therefore require the generation and analysis of double and triple knockout lines. The project ran for eight months in Cologne with MC-IEF funding and is being continued by the fellow outside Europe with different funding.
The aim of the project was to identify proteases that are responsible for leaf senescence in plants, which involves a massive degradation of rubisco, the most abundant protein in the world. Remarkably, the proteases involved in this proteolytic process are not yet known. The approach was to use activity-based profiling with probes for proteases to identify the protease activities that are up-regulated during leaf senescence in Arabidopsis, and subsequently to address their role in senescence using reverse genetic approaches.
Probes for the proteasome, serine proteases and vacuolar processing enzymes did not reveal significantly increased activities of any of these enzymes during senescence. In contrast, probes for papain-like cysteine proteases showed an increased activity of some of these enzymes during senescence, predominantly caused by increased levels of one protease called RD21. Additional senescence-related proteases identified by mass spectrometry included SAG12, which is used as a transcriptional marker for senescence. Surprisingly, Arabidopsis mutants lacking RD21 or other senescence-related proteases did not have phenotypes in senescence assays, such as chlorophyll degradation, despite the fact that they have significantly reduced protease activities in senescing leaves.
These data suggest that these proteases act redundantly with other senescence-related proteases. Further work would therefore require the generation and analysis of double and triple knockout lines. The project ran for eight months in Cologne with MC-IEF funding and is being continued by the fellow outside Europe with different funding.